A 32-stud plate is almost exactly 10 inches
When my boys were younger, I set up a 4’x8′ LEGO city in my basement starting with a piece of plywood and a can of green spray paint for a combined cost of $9. Assuming that 10″x10″ baseplates cost $5 each, a quick calculation shows that covering the same area in a double layer of baseplates would cost about $460.